1. Technical Field
The present invention relates to an external storage medium mounted on a vehicle including a passenger car, freight car, or an emergency car such as an ambulance car. More particularly, it relates to a car disk drive unit, such as a hard disk (HD) drive. In addition to a car disk drive unit carried in a car, it also relates to a car disk drive unit mounted on a vehicle, such as a train, a motorcycle, a vessel, an airplane or a disk drive unit mounted on a vending machine and a point-of-sale terminal located outdoor or an outdoor video recorder and the like.
2. Description of the Related Art
As information apparatuses including navigation systems, Electronic Toll Collection System (ETC), car automation or mobile apparatuses have become common, disk drives for reading and writing data associated with characters, audio, and video and the like to the hard disk, replacing conventional tapes or the like have been proposed as their external storage media. This aims for a reduction in access time and a tremendous increase in storage capacity in view of an increase in information content to affect the above-mentioned information apparatuses.
As shown in FIG. 9, a conventional hard disk drive (HDD) comprises a disk 150 wherein magnetic layers are formed; a spindle motor 9 for rotating the disk 150; a fluid lubricating bearing (not shown) for supporting a rotor 91 of the spindle motor 9; an actuator 10 disposed on one side of the disk 150; a swing arm 16 rotated by the actuator 10; and a magnetic head 17 which is in proximity to a track 151 of the disk 150.
The following problems arise when mounting a conventional HDD on a vehicle. More particularly, the temperature in a cabin and a trunk of a car may go down to −30° C. or lower in cold areas and in winter due to a profound effect exerted by the environment in the car. In warm areas and in summer, the temperature may go up to 60° C. or higher. When the temperature in a car goes down, an extreme increase in viscosity of a tightly sealed lubricant on the fluid lubricating bearing causes the addition of an excessive load to the spindle motor, which prevents the disk from rotating smoothly. As a result, a malfunction occurs on the disk drive.
Further, as the temperature in the car drops, dew condensation generates in the car. Particularly, electronic parts which comprise an HDD easily have dew condensation because of being made of metal materials with a low specific heat, which arises a problem of corrosion. This problem also arises when cooling in the car by starting an air conditioner in summer or the like.
Further, as the temperature in the car drops, dew condensation generates in the car. Particularly, electronic parts which comprise an HDD easily have dew condensation because of being made of metal materials with a low specific heat, which arises a problem of corrosion. This problem also arises when cooling in the car by starting an air conditioner in summer or the like.
This results in deterioration of physical properties of a lubricating film (oil film) to absorb or decrease vibrations from outside, so that the shaft of the disk 150 will shake by the vibrations caused by running of the car. If such vibrations become fiercer, the disk 150 will so vigorously swing to the degree that the magnetic head 17 is unable to write data or read data. Alternatively, the disk 150 and the magnetic head 17 may be destroyed by their collision.
Hard disks have been mainly described so far, but specific working proof temperatures of disk drive units, such as compact disks (CD) and DVD (Digital Video Disks) have been decided and there may be a problem that they cannot normally operate when being mounted on-vehicle in the above-mentioned environments.
It is an object of the present invention to provide a car disk drive unit operating in a stable condition which is hardly affected by temperature changes in a car.